Go to Hell! Lovecraft Add-On
I wrote this as an add-on to the existing rules of Go To Hell! which already exist here. I claim no credit for that game, some Anon did it. This add-on allows players to have Lovecraftian monsters in their game, just in case having hellish demons wasn't already batshit to begin with.
Lovecraftian creatures use Ritual (which will be known from now on as RIT) points for summoning. RIT points are earned, like the name suggests, through rituals. A lesser ritual, requiring at least 1 poor critter's death, a bit of light-hearted chanting and a few basic arcane sigils, will give you 2 RIT points. A greater ritual, requiring at least 1 poor sod's death, lots of angry chanting and symbols so eldritch and twisted that the eyes hurt and the soul twists at the sight of them, will give you 5 RIT points. These rituals often draw the police, because of the tendency towards murder and animal abuse, meddling kids, strange cultists, and worst of all, strange creatures which are drawn to magic. In the likelihood that you kill a demon, the Great Old Ones will generally be chuffed enough to give you some RIT - D4+1 for a lesser demon and D6+2 for a greater demon, the dice-rolling representing the mood they seem to be in at the time. When battling, the amount of RIT spent is the same as the amount of retries you get, just like Luxuria. Every time you fill your capacity for RIT from below 4, the maximum capacity increases by 1, for example, you get 10 RIT points from 0, maximum capacity increases to 11, get to 11 from below 4 RIT, maximum capacity increases to 12, and so on. This represents the increased amounts of power made available to you by the Great Old Ones for serving them so well.
Mind Break Test
This test represents the mind-fucking nature of many of the Lovecraftian entities. When the rules call for a Mind Break test, roll a D10. If you rolled under or equal to the number of Sanity points the person in question has, they're okay. If you rolled over, then the repercussions listed in that part of the rules will apply. If the person doing the test has more then 10 Sanity points, they automatically pass.
NPCs will sometimes have to do Mind Break tests. Generally, a well-disciplined person like a soldier, or someone used to demons and the like, would have 10 sanity points, a normal person would have 9, a drunk or drugged person 8, and a weird cultist would have 6 or 7. Narrators can change these values if necessary.
This category covers little things like Shoggoths, Unnamables, Night-Gaunts, and the like. You can generally have some freedom with what your creature is, but keep it Lovecrafty. If in doubt, check your Call of Cthulhu (or equivalent) monster list for ideas, or think of a weird thing and throw some tentacles on it.
These things are slightly stronger than lesser demons, but will obey their master, provided that they are given enough RIT points. They will take 2 RIT points per summon, but can be summoned with 1 RIT point in a pinch. When they are summoned using 1 RIT point, the person doing the summoning must do a Mind Break test. If they pass, the creature behaves as normal. If they fail, the creature will steal 1 Sanity point from the person doing the summoning, before behaving as normal.
A lesser creature will not demand Contract Limits, but will instead randomly demand RIT points to feed the Great Old Ones (Who gave it to you in the first place). At the beginning of very turn a player with a lesser creature has, they must roll 1d6. On a roll of 1, they lose 1 RIT point. If they don't have enough, they lose 1 Sanity instead.
Now we get to the big ol' heavyweights, the Lesser Gods. These are Great Old Ones, just ones which are weaker than the others. However weak they are though, they still are immensely powerful. There are two ways they can be summoned - With a human host or fully formed.
If you find a human host (It can be any human, either living or very recently dead with a mostly intact body who has been untainted by magic, be that demons, ancient astral magic, or similar), then you can perform a short ritual to allow the Lesser God into their body (Note: They have to be unable to move and in a vacant state of consciousness, so either very recently dead, asleep, drugged or unconscious). This allows the Lesser God to move amongst humans without driving them nuts, unless the person looks directly into their eyes or notices the God's true nature in another way. If that happens, follow the rules (Later on in this guide) for if they see a Lesser God in their true form. Their power will be diminished to the point of being only slightly stronger than a greater demon, and they will be only as resilient as their weak, fleshy host body can allow, so if the head is destroyed, they will leave the host. However, the God will obey your commands, causing you some grief in the process, but on a lesser scale compared to when they are in their natural form. The possession method costs 5 RIT points.
If you want to bring the God into being in their true form, they are brought into this dimension with their full power and capabilities. A chant, incantation, sigil or the like can be used to stabilise the God before they appear. If the God is not stabilised before it is summoned, it will force you, alongside any onlookers, to do a Mind Break test. Failing the test will temporarily reduce you to 2 Sanity for the rest of the scene, while the God rampages around freely until the end of the scene. You will have lost a Sanity point when you come to. Passing the test will make you lose a Sanity point, but other than that, everything will be normal (Well, as normal as things can be with a fucking Lesser God around). If the God was stabilised, then you will lose 1 sanity point, but only onlookers will have to do Mind Break tests. Lesser Gods in their true form will obey your commands, but will destroy, kill, devour, and drive insane pretty much everyone in the way. It costs a whopping 10 RIT points to summon a Lesser God into this dimension. If a Lesser God wins a fight against another demon or other entity, it can't kill its Holder, but can make them go crazy (Lower them to 2 Sanity points).
Lesser Gods will demand RIT points for themselves in a similar way to Lovecraftian Creatures. THe player controlling a Lesser God rolls a D6 at the beginning of their turn, on a roll of 1, the God claims 2 RIT points for themself. If that player doesn't have enough, the God will claim Sanity points too (e.g. player only has 1 RIT point, they lose that and 1 Sanity, player has 0 RIT points, they lose 2 Sanity points)
You may wonder how Lovecraftian players deal with so many Sanity penalties. The answer: players with Lesser Gods and Lovecraftian creatures start with 15 Sanity points, not 10, and can have a maximum of 15 Sanity. They can also increase the amount of Sanity available, by going from 4 or less Karma to 15 again.
Whenever you use 1 RIT point, you lose 1 Karma. This is to represent the karma lost as a result of the unspeakable things you had to do to get those RIT points in the first place. So by summoning Nyarlathotep's little brother, you burn out ALL of your Karma in one go. So you better be careful about when you whip your Lesser God out.